1. Field of the Invention
This invention relates to a method for fabricating thin film semiconductor superlattice heterostructures and the resulting structures and devices obtainable thereby and more particularly to the production of quantum-well structures on non-planar substrates.
2. Description of the Prior Art
"Thick" (&gt;500 .ANG.) epitaxial layers have been grown on nonplanar substrates by various growth techniques, e.g., liquid phase epitaxy (LPE), molecular beam epitaxy (MBE), and organometallic chemical vapor deposition (OMCVD). In all cases, the nonplanarity of the substrate gives rise to lateral thickness variations in the epitaxial layers. Such laterally patterned structures have been useful for optical wave guiding (essentially because the wavelength of light is comparable to the layer thicknesses involved).
Ultra-thin (&lt;500 .ANG.) epitaxial layers have been grown on planar substrates. For such thin layers (i.e. layers whose thickness is comparable to the deBroglie wavelength of charge carriers) quantum-size effects in one dimension (along the growth direction) modify the material properties (e.g., bandgap and refractive index). Hence, by tailoring the thickness of the epitaxial layers, it has been possible to vary the resulting superlattice (or quantum well) material properties. For example, selection of the superlattice (SL) periodicity results in selection of the material bandgap. In addition, these superlattices give rise to new features, e.g., enhanced nonlinear optical properties. Furthermore it has been shown that the SL period (or layer thicknesses) in the direction of layer growth, allows one to fabricate structured materials in which the physical properties in the direction normal to the substrate plane differ based upon the SL period. Devices which rely not only upon the new properties of the SL materials, but also on quantum-size effects that occur in the individual layers, have also been demonstrated, e.g., quantum-well lasers, resonant tunneling devices, quantum-confined Stark effect modulators, etc.
The production of SL or quantum-well devices having superlattice structures which are more than one dimensional and/or which vary laterally in thickness is desirable in order to obtain devices having different and/or enhanced physical properties and having new and different capabilities than prior art quantum effect devices.